We propose the Borderline Personality Disorder (BPD) as a unique and clinically relevant model for the study of suicidal behavior. BPD is a syndrome defined by affective instability, recurrent suicidal behavior and impulsive aggression in a context of chronic chaotic interpersonal relationships. It is among the most lethal of psychiatric disorders, with a rate of completed suicide of 3 - 9.5%. BPD is highly prevalent, accounting for 11% of outpatients and up to 23% of admissions to psychiatric hospitals. Borderline patients present a high incidence of suicidal behaviors in the group as a whole and a high frequency within individuals. This disorder is also characterized by a high frequency and broad diversity of "low lethality" self destructive behaviors providing a wide range of severity of attempt characteristics (e.g. objective planning, subjective intent and degree of medical damage). There have been no prospective multi-dimensional studies of suicidal behavior in this disorder. There is no treatment of choice for the suicidality of the borderline patient. We propose a first comprehensive multidimensional study-of the clinical, biological and psychosocial risk factors for suicidal behavior in a cohort of 120 criteria defined borderline inpatients, followed prospectively for 1 year. Two thirds will be prior suicide attempters and one-third lifetime non-attempters. We will compare groups at baseline on the following putative risk factors: a) Co-morbidity with affective and substance use disorders; b) disruption of interpersonal relationships, loss of social supports: c) degree of characterologic impulsivity and aggression; d) history of suicide attempts; e) absence of psychiatric treatment- f) decreased central serotonergic functioning. We will characterize the central serotonergic function of patients with BPD through a study of CSF 5-HIAA and Fenfluramine challenge, as these measures have previously indicated a strong inverse relationship between serotonin and suicidal behavior ih BPD. In addition to the prospective study of suicidal behavior in BPD. We will perform cross-sectional analyses comparing BPD attempters and non-attempters with normal controls, schizophrenic and depressed patients available in similar format through the Suicide MHCRC of WPIC at no additional cost to this proposal.